Locking mechanisms for door assemblies have long been used on a wide variety of doors to a chamber and/or room that is desired to be isolated. Examples of various types of locking structures are shown in U.S. Pat. Nos. 1,269,572; 2,664,611; 4,114,933; and 4,342,207.
However, if the chamber and/or room that is to be secured requires an ability to maintain a greater pressure from within the chamber than exists outside the chamber, additional pressure related considerations must be taken into account. Such pressure vessel closure assemblies have long been known and include a wide variety of structures as shown in U.S. Pat. Nos. 2,010,200 and 3,258,151. Of the types of pressure closure assemblies for pressure vessels utilizing some type of annular or radially expanding element, some examples are shown in U.S. Pat. Nos. 2,196,895; 4,102,474 and 4,315,577. However, so far as known, all of the aforementioned pressure vessel closure members require centrally mounted and/or operated mechanisms for effectuating a radially expanding locking element. In some cases, as for example with U.S. Pat. No. 4,102,474, a central portion of a closure member is required to be maintained at a pressure in order to properly actuate particular elements thereof in order to accomplish the locking operation. In like fashion, U.S. Pat. No. 4,315,577 discloses a centrally mounted operator rotating in such a fashion that the locking elements are individually and independently moved outwardly based upon movement of a pin in a spiraling track.
Thus, so far as known, no pressure vessel closure member is available that provides an annular locking ring assembly having an unobstructed central area of a size greater than one-half the outside diameter of the closure member which permits a suitable viewport and/or other non-locking features to be incorporated with the pressure vessel closure member.